If you read my previous post, you'll be interested by this one. Indeed, I have discovered that the idea introduced in the previous post is working but not practical at all since it does not work with type synonym definitions. But, without synonyms, you can't really write the kind of types required to do http content-type comparison at the type level. By luck, some additional type hacking is solving the problem. Moreover, I think it can be useful to show in a very informal way a few applications of computations at type level. It is not so hard (but not totally trivial. I had to make several experiments to get it right).

 

In my last post, I was writing about the use of coproduct of free monads to do content-type dispatching in a web monad. It was working but it was not the right approach. I changed everything and introduced a lattice of lists at the type level to track hierarchical dependencies between formats and do content-type dispatching thanks to type information. I also added a few other features to my Web Monad.

 

From time to time, I continue my experiments with Haskell and web development and try to build my own framework. I will never release anything because I am just exploring a few ideas.

Recently, I experimented with a common problem : when a client is getting an URL, it is communicating the formats it wants with some preference values. The server should return the best format according to what is requested by the client and what is supported by the server.

 

I am pleased to release a new version of my PDF library for Haskell and an example showing what's possible with the library : a magazine generated in an automatic way with Haskell.

The parsing for the magazine has not yet been debugged totally and the image layout algorithm is currently very simple. The text formatting in columns is not always ok because I have not yet implemented an hyphenation algorithm. But, the result, still in beta, is good.

 

I have finally released HPDF 1.1 with some typesetting features. More details are in this post. It is very experimental but working. I am not happy at all with the API of HPDF but I have no choice. I need, for another project, to add features as fast as possible. I'll think about the elegance of the API later even if I need to change lots of things in HPDF (not really a good development methodology I agree). In addition to the typesetting features, I corrected lots of problems, optimized the code and changed a little bit the image API.